The proposed project involves developing a targeting construct that will generate tissue-specific expression of a constitutively active form of protein kinase A (PKA). Examination of the expression of this unregulated protein in embryonic stem cells (ES cells) compared to cells expressing either normal or decreased levels of PKA will allow us to determine the role of PKA in ES cell proliferation and differentiation into distinct cell fates. Contribution of these targeted ES cells to the germline of mice will permit expression of this protein in specific tissues under experimentally controlled conditions. Preliminarily, we plan to study the effect of this constitutively active PKA enzyme in the regulation of adiposity and weight regulation, processes that are known to involve PKA. We predict that mice expressing this constitutively active form of PKA in adipose tissue will exhibit a lean phenotype, contributing to our understanding of body weight regulation and suggesting possible treatments for obesity in humans.